NEWS ARCHIVE

Scientists have looked deeper into the Universe than ever before and found massive black holes growing in distant young galaxies, according to a paper published in the 7 April issue of the scientific journal Nature. These findings provide new insights into the construction of todays largest galaxies and their central black holes.

Over the last decade, astronomers have found that the total mass of stars in galaxies such as the Milky Way corresponds directly to the size of their central black holes. This relationship suggests that galaxies and their black holes grew at the same time. However, until now, this idea had lacked direct observational support.

Speaking on Wednesday 6 April at the Royal Astronomical Societys National Astronomy Meeting, lead author of the study, Dr. David Alexander (Institute of Astronomy, University of Cambridge) will explain how the team studied galaxies originally identified by the James Clerk Maxwell submillimetre telescope and then used NASA's Chandra X-ray Observatory to find strong X-ray glows produced by hot gas swirling around the growing black holes.

The first crucial step in understanding the nature of these galaxies was to measure their properties with the 10-metre Keck optical telescope in Hawaii. The Keck observations indicated that these galaxies were being seen more than 10 billion years ago when the Universe was just a quarter of its current age. The Keck observations allowed us to determine that these galaxies were forming their stars at a colossal rate, said Dr. Alexander.

Our detection of X-ray emission with Chandra indicates that their black holes were also growing at the same time. These findings provide direct observational support for the simultaneous growth of large galaxies and their black holes. These galaxies are very faint and it is only with deep observations of the Universe that they can be detected at all, said Professor Ian Smail of the University of Durham, co-author of the study. Before these deepest ever X-ray observations we had great difficulty in identifying growing black holes in these galaxies.

The X-ray observations also showed that the black holes are surrounded by a dense shroud of gas and dust. This is probably the material that will be consumed by the growing black holes. What was the catalyst that kick-started this joint growth? Deep observations by the Hubble Space Telescope have indicated that these galaxies are in major mergers involving collisions between two galaxies of similar size.

A recent sophisticated computer simulation, performed by Dr Tiziana Di Matteo of Carnegie Mellon University and collaborators, has shown that these major mergers drive material towards the central regions of galaxies, producing stars and providing the fuel that feeds the black hole and enables it to grow.

These recent observations are in good agreement with our simulation, said Dr Di Matteo. It is exciting that we seem to be converging on a consistent picture of galaxy formation with both observations and theory. The new results shed further light on how our Galaxy could develop in the future. Three billion years from now, we may see similar events taking place much closer to home. The Milky Way is on a collision course with the nearby Andromeda galaxy. The eventual collision will cause the black holes and galaxies to merge, producing a more massive black hole and a larger galaxy. Funding for this research was provided by the Royal Society, PPARC, and NASA.

The James Clerk Maxwell Telescope (JCMT) is operated on behalf of the United Kingdom, Canada & Netherlands by the Joint Astronomy Centre. With its 15-m (50-ft) diameter dish, the JCMT detects light with submillimetre wavelengths, between infrared light and radio waves on the wavelength scale.

The W. M. Keck Observatory is operated by the California Association for Research in Astronomy.

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